The compositions according to the present invention make it possible a sheltering action to be achieved, which is kept unchanged for a very long time, also when the treated material is exposed to drastic environmental conditions of decay and ageing.
It is well-known that many materials tend to decay with time and to become, for example, extremely porous and incoherent, before getting completely destroyed, due to chemical actions performed by the surrounding environment, or owing to also natural causes of decay and ageing. Typical examples of materials which undergo such an action are any kinds and types of stones, such as bricks, marbles, building materials, and so forth.
The problem of the preservation of these materials is of basic importance in those cases in which one wishes to preserve the object or built structure with its original appearance, and replacing it to a more or less integral extent is not desired. This problem arises, e.g., in case of cultural, artistic, historical and archaeological goods, whose inheritance has to be preserved for a time which should be as long as possible.
It is well-known that the materials which are more subject to such effects of intense decay are lithoidal monuments such as churches, palaces, built structures, and so forth, which, by being in continuous contact with the more or less polluted atmosphere of towns and/or of the surrounding environment, undergo continuous attacks by chemical agents, such as sulfur oxides or nitrogen oxides which, in the presence of atmospheric humidity, exert an action which modifies to a substantial extent the nature of the materials they were built with. These chemical attacks, combined with the natural temperature variations, cause changes in colour, or the formation of crusts, scales, thin strips, crevices, and so forth, with the concerned materials consequently undergoing a progressive, continuous and inexorable loss of cohesion, and portions of materials getting lost day after day.
In this case, the intervention aiming at preserving the object or built structure requires a preliminary cleaning and a subsequent step of protective treatment, during which the operators try to protect the various constituting elements or parts, aiming at preventing aggressive agents from attacking the protected object or structure and its more significant portions, such as decorations, relieves, and so forth.
For the purpose of achieving such a protection, it is known to coat or soak the concerned object or structure, or material, with polymeric film-forming substances, such as acrylic, vinylic, siliconic resins, and so forth, showing a good adhesive power, a good resistance to atmospheric agents and a fairly good resistance to ageing due to the action of light and of other atmospheric agents. The main drawback shown by these polymeric substances is that they form a film which, even if is kept very thin, is not permeable to air, vapours and other gases. Such an impermeable coating causes vapours to accumulate inside the material, salts to concentrate and a whole range of processes to take place which may irreparably damage the treated material to an even more evident extent. In fact, it is known that the transpiration of a material, such as stone, brick, marble, and so forth, is of basic importance for the purposes of its correct and long-lived preservation.
In Italian patent application 21018 A/89 it was found that polyurethanes with hydroxy functionality, whose chains contain moieties of perfluoroether nature, are products showing the above said characteristics and which, beside being colourless and having good adhesion properties and optimum characteristics of resistance to light, moisture, water and atmospheric agents, do not substantially modify the permeability to gases and vapours and furthermore show characteristics of being not film-forming and of reversibility.
Unfortunately, it was observed that applications of such products to lithoidal materials with a high moisture content, like stone materials may be immediately after rain, are difficult and usually ineffective, in that the hydrophobic nature of the products constitutes a hindrance to a correct application thereof.
The purpose of the instant invention is of providing a composition for protecting lithoidal materials which, besides being endowed with the above described characteristics, is suitable for being applied onto substrates having a high moisture content.